F E R TI L I T Y MA T T ER S
Perinatal outcomes after assisted reproductive technology treatment in Australia and New Zealand: single versus double embryo transfer Yueping A Wang, Elizabeth A Sullivan, David L Healy and Deborah A Black
S
ince 2002, the Reproductive Technology Accreditation Committee in Australia and New Zealand has advocated reducing the number of embryos transferred to women undergoing assisted reproductive technology (ART) treatment, the aim of The Medical Journal of with Australia ISSN: 1 minimising the number of multiple births. 0025-729X 2 March 2009 190 5 234-237 Studies suggest thatJournal the high incidence of ©The Medical of Australia 2009 multiple births following ART is responsible www.mja.com.au Fertility matters for most adverse perinatal outcomes (preterm birth, low birthweight [LBW] and perinatal death).2-4 The high rate of multiple births following ART is largely explained by the number of embryos transferred. Transferring two embryos (double embryo transfer [DET]) increases the odds of a multiple gestation by more than 60 times5 compared with single embryo transfer (SET). Recent studies from Finland concluded that babies conceived by SET had better neonatal outcomes than those conceived after transferring two or more embryos.6 This is the case even among singletons.7,8 Belgium and the Scandinavian countries have endorsed SET as best practice, with Sweden reporting that SET is used in 70% of its embryo transfer cycles.9 The Assisted reproduction technology in Australia and New Zealand 2006 report10 showed that the proportion of embryo transfer cycles using SET had increased from 28.4% in 2002 to 56.9% in 2006 in Australia and New Zealand. Over the same period, the twin rate declined from 18.8% to 11.3%. The aim of our study was to compare the perinatal outcomes of babies conceived by SET with those conceived by DET using data from the Australia and New Zealand Assisted Reproduction Database (ANZARD). METHODS Data source ANZARD is housed at the Australian Institute of Health and Welfare (AIHW) National Perinatal Statistics Unit. Data from fertility centres in Australia and New Zealand, including information on each treatment cycle commenced, pregnancy and birth outcomes, are validated and entered into the database at the National Perinatal Statistics Unit. Data collec234
ABSTRACT Objective: To compare the perinatal outcomes of babies conceived by single embryo transfer (SET) with those conceived by double embryo transfer (DET). Design, setting and participants: A retrospective population-based study of embryo transfer cycles in Australia and New Zealand between 2002 and 2006, using data from the Australia and New Zealand Assisted Reproduction Database. Main outcome measures: Proportion of SET procedures; comparison of SET and DET procedures with respect to multiple births, low birthweight (LBW), preterm birth and fetal death. Results: The proportion of SET procedures has increased from 28.4% in 2002 to 32.0% in 2003, 40.5% in 2004, 48.2% in 2005 and 56.9% in 2006. The multiple birth rate for all babies conceived by SET (4.0%) was 10 times lower than for those conceived by DET (39.1%) (P < 0.01). The average birthweight for all liveborn babies conceived by SET (3290 g) was higher than for those conceived by DET (2934 g) (P < 0.01). The preterm birth rate of all DET-conceived babies (30.3%) was higher than for SET-conceived babies (12.3%) (adjusted odds ratio [AOR], 3.19 [95% CI, 3.01–3.38]). All babies conceived by DET were more likely to be stillborn than those conceived by SET (AOR, 1.49 [95% CI, 1.21–1.82]). Singletons conceived by DET were more likely to be born preterm than singletons conceived by SET (AOR, 1.13 [95% CI, 1.05–1.22]). Liveborn singletons conceived by DET were 15% more likely to have LBW than liveborn singletons conceived by SET (AOR, 1.15 [95% CI, 1.05–1.26]). There was no significant difference in fetal death rate between DET- and SET-conceived singletons. Conclusion: The increase in proportion of SET procedures has resulted in a lower rate of multiple births and in better perinatal outcomes in Australian and New Zealand assisted reproduction programs. MJA 2009; 190: 234–237 For editorial comment, see page 232
tion on pregnancy and neonatal outcomes varies between fertility centres but includes follow-up with the patient or clinician and the use of routine data from the relevant health department. Information on pregnancy outcomes and neonatal outcomes is missing for about 2% of clinical pregnancies recorded in ANZARD. We carried out a retrospective analysis of ANZARD data on embryo transfer cycles and subsequent pregnancy and baby outcomes for the period 2002–2006.
• Stage of embryo development. Embryos were classified as cleavage-stage embryos or blastocysts. • Gestational age. Defined as the number of completed weeks of gestation of the fetus, gestational age was calculated from the formula [(pregnancy end date minus embryo transfer date) plus 16 days]. • Perinatal outcomes. Outcomes examined were LBW (birthweight < 2500 g in liveborn babies), preterm birth (gestational age < 37 completed weeks) and fetal death (stillbirth) (number of fetal deaths per 1000 births).
Outcome measures and definition of terms • Maternal age. Maternal age was expressed as the number of completed years at the time of ART treatment. • Type of embryo. Embryos were classified as fresh (never frozen) or thawed (following cryopreservation). MJA • Volume 190 Number 5 • 2 March 2009
Statistical analysis The number and proportion of SETs and DETs were stratified by women’s age (< 35 years, 35–39 years or ⭓ 40 years) and described by year. SET and DET were compared with respect to perinatal outcomes for all babies,
F E R TI L I T Y MA T T ER S
with t tests used for continuous variables and χ2 tests used for categorical variables. Univariate and multivariate logistic regression analyses were used to examine the likelihood of adverse perinatal outcomes. Data were analysed using SPSS software, version 16.0 (SPSS Inc, Chicago, Ill, USA). Ethics approval Our study was approved by the Human Research Ethics Committee of the University of New South Wales. RESULTS Number of embryos transferred In Australia and New Zealand over the period 2002–2006, there were 172 190 cycles in which embryos were transferred: 73563 SET cycles (42.7%), 93 429 DET cycles (54.3%) and 5198 cycles (3.0%) in which three or more embryos were transferred. Women aged 40 years or older tended to have a lower proportion of SETs compared with younger women. The overall proportion of SETs increased from 28.4% in 2002 to 32.0% in 2003, 40.5% in 2004, 48.2% in 2005 and 56.9% in 2006. Between 2002 and 2006, the proportion of SETs increased from 28.7% to 66.2% for women aged < 35 years, from 27.5% to 54.4% for women aged 35–39 years, and from 29.1% to 42.5% for women aged ⭓ 40 years. Perinatal outcomes Over the period 2002–2006, 40 483 babies (73.0% singletons, 26.3% twins, 0.7% triplets or higher) were born to women who had either SET or DET cycles in Australia and New Zealand. Of these babies, 14 022 (34.6%) were conceived by SET and 26 461 (65.4%) by DET. The multiple birth rate for babies born to women who had SET cycles (4.0%) was about 10 times lower than for those born to women who had DET cycles (39.1%) (P < 0.01; χ2 = 5768.3; df = 1) (Box 1). The overall preterm birth rate was 24.1%. The mean birthweight of liveborn babies was 3058 g, with 19.2% of babies having LBW. There were 520 fetal deaths (12.8 fetal deaths per 1000 births) after either SET or DET. Type of embryo
Liveborn babies conceived after thawed embryo transfer cycles had a significantly lower rate of LBW than those conceived after fresh embryo transfer cycles, regardless of whether they were SET or DET. Similarly, the rate of preterm birth was significantly lower for babies conceived after thawed embryo
1 Number (%) of babies born to women following SET or DET procedures, Australia and New Zealand, 2002–2006 Singletons
SET
DET
Total
13 468 (96.0%)
16 100 (60.9%)
29 568 (73.0%)
Multiples
554 (4.0%)
10 361 (39.1%)
10 915 (27.0%)
Twins
532 (3.8%)
10 090 (38.1%)
10 622 (26.3%)
Triplets or higher
22 (0.2%)
271 (1.0%)
293 (0.7%) ◆
DET = double embryo transfer. SET = single embryo transfer.
2 Perinatal outcomes of babies born following SET or DET procedures, by type of embryo, Australia and New Zealand, 2002–2006 Total Number and liveborn type of embryo babies
Proportion of LBW liveborn babies
P* < 0.01
Proportion of preterm Total births (all babies babies)
P*
Fetal deaths/ 1000 births (all babies)
< 0.01
10.1
P*
SET Fresh embryo
9 121
9.5%
Thawed embryo
4 736
7.3%
18 402
27.7%
7 620
17.7%
9 229
12.9%
4 793
11.2%
0.79
9.6
DET Fresh embryo Thawed embryo
< 0.01
18 737
32.5%
7 724
25.0%
< 0.01
16.1
< 0.01
10.4
All Fresh embryo
27 523
21.7%
Thawed embryo
12 356
13.7%
< 0.01
27 966
26.0%
12 517
19.7%
< 0.01
14.1
< 0.01
10.1
DET = double embryo transfer. LBW = low birthweight. SET = single embryo transfer. * χ2 test, df = 1.
◆
3 Perinatal outcomes of babies born following SET or DET procedures, by stage of embryo development, Australia and New Zealand, 2002–2006 Number and stage of embryo development
Total liveborn babies
Proportion of LBW liveborn babies
P*
Proportion of preterm Total births babies (all babies)
P*
Fetal deaths/ 1000 births (all babies)
P*
8.7
0.05
SET Cleavage stage
8 877
8.6%
8 971
12.0%
Blastocyst
4 980
8.9%
0.61
5 051
13.0%
22 083
24.9%
0.55 22 447
30.4%
3 939
24.3%
4 014
29.7%
30 960
20.2%
< 0.01 31 418
25.1%
8 919
15.7%
9 065
20.4%
0.08
12.1
DET Cleavage stage Blastocyst
0.36
14.3
0.64
15.2
All Cleavage stage Blastocyst
< 0.01
12.7
DET = double embryo transfer. LBW = low birthweight. SET = single embryo transfer. * χ2 test, df = 1.
transfer cycles than after fresh embryo transfer cycles. The fetal death rate was lower after thawed embryo transfer cycles than after fresh embryo transfer cycles for DET babies but not SET babies (Box 2). Stage of embryo development
About 5% of babies conceived by single blastocyst transfer were multiples, which is MJA • Volume 190 Number 5 • 2 March 2009
0.55
13.5 ◆
significantly higher than the 3.4% for babies conceived by single cleavage-stage embryo transfer (P < 0.01). The multiple birth rate was 42.1% for babies conceived by double blastocyst transfer compared with 38.7% for babies conceived by double cleavage-stage embryo transfer (P < 0.01). Babies conceived by blastocyst transfer had a significantly lower rate of LBW and 235
F E R TI L I T Y MA T T ER S
preterm birth than those conceived by cleavage-stage embryo transfer. Babies conceived by single blastocyst transfer had slightly higher rates of preterm birth and fetal death than those conceived by single cleavagestage embryo transfer. The fetal death rate was 15.2 per 1000 births for babies after double blastocyst transfer cycles, compared with 14.3 per 1000 births for babies after double cleavage-stage embryo transfer cycles, but the difference between the two was not significant (Box 3). Birthweight
The mean birthweight for all liveborn babies conceived by SET (3290 g) was significantly higher than the mean for those conceived by DET (2934 g) (P < 0.01). Term liveborn singletons conceived by SET had significantly higher mean birthweight (3430 g) than those conceived by DET (3401 g), regardless of sex (P < 0.01). There was no significant difference between SET- and DET-conceived babies in mean birthweight of liveborn singletons born at 32–36 weeks of gestation (Box 4). Liveborn babies conceived by DET were 3.6 times more likely to have LBW than those conceived by SET (Box 5). Liveborn singletons conceived by DET had a significantly lower mean birthweight (3287 g) than singletons conceived by SET (3332 g) (P < 0.01). Consistent with this, liveborn singletons conceived by DET were 15% more likely to have LBW than singletons conceived by SET (adjusted odds ratio [AOR], 1.15 [95% CI, 1.05–1.26]) (Box 5). Preterm birth
The preterm birth rate of all babies conceived by DET was 30.3%, compared with a rate of 12.3% for babies conceived by SET. Singletons conceived by DET were 13% more likely to be born preterm than those conceived by SET (Box 5).
DISCUSSION Consistent with other studies,6,8,11 we found that babies conceived by SET had better perinatal outcomes than those conceived by DET. This was the case even for singletons. Regardless of maternal age, DET-conceived singletons had 15% greater odds of LBW and 13% greater odds of preterm birth than SET-conceived singletons. Our analysis showed that the multiple birth rate for babies conceived by DET was nearly 10-fold higher than for babies conceived by SET. Multiple births are strongly associated with poorer perinatal outcomes.4,12 LBW and preterm birth have been shown to be directly related to fetal and neonatal death, and short- and long-term morbidity and mortality.13,14 The rationale for favouring DET over SET, until recently, has been that the transfer of two or more embryos results in a higher clinical pregnancy rate than the transfer of only one embryo, especially in younger women.15 However, a higher clinical pregnancy rate does not mean better perinatal outcomes for the baby. Multiple gestations not only increase the risk for babies, but also for mothers.16,17 Threatened miscarriage, hyperemesis, thromboembolism, hypertension, haemorrhage and maternal mortality are all significantly increased in multiple gestations.17 There is also a greater risk of depression and marital decline after multiple gestations.16 In addition, multiple gestations place a greater economic and social burden on the parents and on the health care system.18,19 In Australia in 2003, the average combined cost
4 Mean birthweight of liveborn singletons following SET or DET procedures, by gestational age, Australia and New Zealand, 2002–2006 SET
Perinatal outcomes of multiples
Unlike singletons, multiples conceived by DET had better perinatal outcomes than those conceived by SET (Box 5). However, more than half of liveborn multiples (whether conceived by DET or SET) were LBW and 60% of multiples were born preterm. 236
DET
Number of Mean birthweight Number of live births (g) (SD) live births
Fetal death
Babies conceived by DET were more likely to be stillborn than those conceived by SET (AOR, 1.49 [95% CI, 1.21–1.82]). The fetal death rate for singletons conceived by DET (10.9 deaths/1000 births) was slightly higher than the rate for singletons conceived by SET (8.6 deaths/1000 births), but the difference was not significant (Box 5).
of infant and maternal birth admission following ART treatment was $8053 for singletons compared with $23 214 for twins and $90 742 for higher-order multiples.20 One of the findings of our study was that preterm birth and LBW were less likely to occur in babies conceived by thawed embryo transfer than fresh embryo transfer. This is consistent with other studies3,21 showing that cryopreservation does not adversely affect fetal development or perinatal outcomes, but in fact appears to have a protective effect. The better outcomes of babies conceived from frozen embryos are likely to be related to the more similar ovarian and uterine conditions in thawed embryo transfer cycles to those for non-ART conceptions.21 Twins conceived by SET are considered to be monozygotic twins.22 In general, monozygotic twins have worse perinatal outcomes than dizygotic twins.23 Consistent with other studies,22 our data showed a significantly higher rate of twins following blastocyst transfer (both SET and DET) than cleavage-stage embryo transfer. But overall outcomes were more favourable for babies following blastocyst transfer than cleavage-stage embryo transfer. This may largely be explained by more DET in cleavage-stage embryo transfer cycles than in blastocyst transfer cycles, and hence an overall higher multiple birth rate following cleavage-stage embryo transfer cycles. A significantly lower LBW rate was observed for singletons following blastocyst transfer in our study, which supports the suggestion that the blastocyst culture could have had an impact on higher birthweight.24
Mean birthweight (g) (SD)
P*
Female singletons < 32 weeks 32–36 weeks ⭓ 37 weeks
98
1483.3 (900.0)
146
1225.0 (757.1)
465
2559.4 (548.3)
614
2518.7 (574.3)
0.02 0.24
5 835
3364.6 (467.7)
7 071
3333.1 (475.5)
< 0.01 0.24
Male singletons < 32 weeks
115
1367.3 (752.4)
168
1264.5 (703.3)
32–36 weeks
569
2631.7 (557.1)
721
2616.9 (560.6)
0.64
6 117
3492.8 (485.3)
7 021
3469.3 (493.0)
0.01 0.01
⭓ 37 weeks All singletons < 32 weeks
214
1422.4 (822.1)
315
1247.1 (727.0)
32–36 weeks
1 034
2599.2 (554.0)
1 337
2571.6 (568.6)
0.24
⭓ 37 weeks
11 953
3430.2 (481.1)
14 105
3400.8 (489.2)
< 0.01
DET = double embryo transfer. SET = single embryo transfer. * t test.
MJA • Volume 190 Number 5 • 2 March 2009
◆
F E R TI L I T Y MA T T ER S
5 Perinatal outcomes of babies born following SET or DET procedures, Australia and New Zealand, 2002–2006 SET
DET
OR (95% CI)
AOR* (95% CI)
All babies Low birthweight of liveborn babies
8.7%
24.8%
3.44 (3.23–3.68)
3.55 (3.32–3.80)
Preterm birth of all babies
12.3%
30.3%
3.10 (2.92–3.28)
3.19 (3.01–3.38)
Fetal death of all babies †
9.9%
14.4%
1.46 (1.20–1.77)
1.49 (1.21–1.82)
Singletons Low birthweight of liveborn singletons
6.6%
7.9%
1.21 (1.11–1.32)
1.15 (1.05–1.26)
Preterm birth of all singletons
10.1%
11.3%
1.14 (1.06–1.23)
1.13 (1.05–1.22)
Fetal death of all singletons†
8.6%
10.9%
1.27 (1.00–1.60)
1.26 (0.98–1.62)
Low birthweight of liveborn multiples
61.4%
51.2%
0.66 (0.55–0.79)
0.60 (0.50–0.72)
Preterm birth of all multiples
67.1%
59.8%
0.72 (0.60–0.87)
0.66 (0.55–0.80)
41.5%
19.9%
0.47 (0.30–0.73)
0.46 (0.29–0.73)
Multiples
†
Fetal death of all multiples
AOR = adjusted odds ratio. DET = double embryo transfer. OR = odds ratio. SET = single embryo transfer. * Adjusted for women’s age, cause of infertility, parity, number of previous assisted reproductive technology treatments, type of embryo, and stage of embryo development. † Number of fetal deaths per 1000 births. ◆
Strengths of our study were the large study population and the two-nation coverage. One limitation was that elective embryo transfer procedures could not be distinguished from all embryo transfer procedures. (A Belgian study has shown that babies conceived by elective SET have better perinatal outcomes than those conceived by DET.25) Another limitation of our study was the potential variability in case reporting. The follow-up information on pregnancy and birth outcomes was collected in a number of ways, including follow-up by the treatment doctors and self-report by patients to fertility clinics. A further limitation was that data on the 2002–2006 study population were incomplete: information on pregnancy and birth outcomes was not stated for 1.7% of clinical pregnancies. Our study confirms that the Reproductive Technology Accreditation Committee’s policy of shifting towards greater use of SET in ART is working. In 2006, more than half of embryo transfer cycles were SETs, resulting in a fall in the multiple delivery rate to 12%, the lowest rate ever reported in Australia and New Zealand. Given the fewer maternal complications, lower rate of adverse perinatal outcomes and higher cost-effectiveness ratio for SET compared with DET, continuing to encourage SET will benefit women and their babies, as well as society in general. ACKNOWLEDGEMENTS The Fertility Society of Australia is the funding body for the ANZARD collection. We acknowledge the contribution of fertility clinics in Australia and New
Zealand in the provision of data to ANZARD.
COMPETING INTERESTS None identified.
AUTHOR DETAILS Yueping A Wang, MPH, Population Health Analyst1 Elizabeth A Sullivan, MPH, MMed(SexHlth), FAFPHM, Perinatal Medical Epidemiologist1 David L Healy, FRACOG, CREI, PhD, Chairman2 Deborah A Black, BSc, MStat, PhD, Associate Professor3 1 Perinatal and Reproductive Epidemiology Research Unit, University of New South Wales, Sydney, NSW. 2 Department of Obstetrics and Gynaecology, Faculty of Medicine, Monash University, Melbourne, VIC. 3 Faculty of Health Sciences, University of Sydney, Sydney, NSW. Correspondence:
[email protected]
REFERENCES 1 Reproductive Technology Accreditation Committee. Code of practice for assisted reproductive technology units. Melbourne: Fertility Society of Australia, 2005. 2 Kissin DM, Schieve LA, Reynolds MA. Multiple-birth risk associated with IVF and extended embryo culture: USA, 2001. Hum Reprod 2005; 20: 2215-2223. 3 Wang YA, Sullivan EA, Black D, et al. Preterm birth and low birth weight after assisted reproductive technology-related pregnancy in Australia between 1996 and 2000. Fertil Steril 2005; 83: 1650-1658. 4 Wang J, Lane M, Norman RJ. Reducing multiple pregnancy from assisted reproduction treatment: educating patients and medical staff. Med J Aust 2006; 184: 180-181. 5 Pandian Z, Templeton A, Serour G, Bhattacharya S. Number of embryos for transfer after IVF and ICSI: a Cochrane review. Hum Reprod 2005; 20: 2681-2687.
MJA • Volume 190 Number 5 • 2 March 2009
6 Poikkeus P, Gissler M, Unkila-Kallio L, et al. Obstetric and neonatal outcome after single embryo transfer. Hum Reprod 2007; 22: 1073-1079. 7 De Sutter P, Delbaere I, Gerris J, et al. Birthweight of singletons after assisted reproduction is higher after single- than after double-embryo transfer. Hum Reprod 2006; 21: 2633-2637. 8 De Sutter P. Single embryo transfer (set) not only leads to a reduction in twinning rates after IVF/ICSI, but also improves obstetrical and perinatal outcome of singletons. Verh K Acad Geneeskd Belg 2006; 68: 319-327. 9 Nygren KG. Single embryo transfer: the role of natural cycle/minimal stimulation IVF in the future. Reprod Biomed Online 2007; 14: 626-627. 10 Wang YA, Dean JH, Badgery-Parker T, Sullivan EA. Assisted reproduction technology in Australia and New Zealand 2006. Sydney: Australian Institute of Health and Welfare National Perinatal Statistics Unit, 2008. (AIHW Cat. No. PER 43.) 11 Heijnen EM, Eijkemans MJ, De Klerk C, et al. A mild treatment strategy for in-vitro fertilisation: a randomised non-inferiority trial. Lancet 2007; 369: 743-749. 12 Ombelet W, De Sutter P, Van der Elst J, Martens G. Multiple gestation and infertility treatment: registration, reflection and reaction — the Belgian project. Hum Reprod Update 2005; 11: 3-14. 13 Bernstein IM, Horbar JD, Badger GJ, et al. Morbidity and mortality among very-low-birth-weight neonates with intrauterine growth restriction. The Vermont Oxford Network. Am J Obstet Gynecol 2000; 182: 198-206. 14 Lira PI, Ashworth A, Morris SS. Low birth weight and morbidity from diarrhea and respiratory infection in northeast Brazil. J Pediatr 1996; 128: 497-504. 15 Dare MR, Crowther CA, Dodd JM, Norman RJ. Single or multiple embryo transfer following in vitro fertilisation for improved neonatal outcome: a systematic review of the literature. Aust N Z J Obstet Gynaecol 2004; 44: 283-291. 16 Klock SC. Psychological adjustment to twins after infertility. Best Pract Res Clin Obstet Gynaecol 2004; 18: 645-656. 17 Campbell DM, Templeton A. Maternal complications of twin pregnancy. Int J Gynaecol Obstet 2004; 84: 71-73. 18 Kjellberg AT, Carlsson P, Bergh C. Randomized single versus double embryo transfer: obstetric and paediatric outcome and a cost-effectiveness analysis. Hum Reprod 2006; 21: 210-216. 19 Callahan TL, Hall JE, Ettner SL, et al. The economic impact of multiple-gestation pregnancies and the contribution of assisted reproductive technology to their incidence. N Engl J Med 1994; 331: 244-249. 20 Chambers GM, Chapman MG, Grayson N, et al. Babies born after ART treatment cost more than nonART babies: a cost analysis of inpatient birth-admission costs of singleton and multiple gestation pregnancies. Hum Reprod 2007; 22: 3108-3115. 21 Shih W, Rushford DD, Bourne H, et al. Factors affecting low birthweight after assisted reproduction technology: difference between transfer of fresh and cryopreserved embryos suggests an adverse effect of oocyte collection. Hum Reprod 2008; 23: 1644-1653. 22 Vitthala S, Gelbaya TA, Brison DR, et al. The risk of monozygotic twins after assisted reproductive technology: a systematic review and meta-analysis. Hum Reprod Update 2009; 15: 45-55. 23 Seibre NJ, Snijders RJM, Hughes K, et al. The hidden mortality of monochorionic twin pregnancies. Br J Obstet Gynaecol 1997; 104: 1203-1207. 24 Thompson JG, Gardner DK, Pugh PA, et al. Lamb birth weight is affected by culture system utilized during in vitro pre-elongation development of ovine embryos. Biol Reprod 1995; 53: 1385-1391. 25 De Sutter P, Van der Elst J, Coetsier T, Dhont M. Single embryo transfer and multiple pregnancy rate reduction in IVF/ICSI: a 5-year appraisal. Reprod Biomed Online 2003; 6: 464-469. (Received 30 Sep 2008, accepted 9 Dec 2008)
❏
237
